Urban wastewater treatment plants (WWTPs) are critical environmental infrastructures, especially in fast-urbanizing cities. Thus, this infrastructure must be carefully designed and constructed with structural and geotechnical aspects. This paper investigates the stability of the sheet pile wall of the Nhieu Loc Thi Nghe WWTP in Ho Chi Minh City, Vietnam, characterized by weak soil conditions and elevated groundwater levels. The aim is to assess the construction of the sheet pile system’s structural behavior against different construction stages, including operational loading conditions. This study focuses on the inclined sheet pile retaining wall and its soil–structure interaction in adverse urban soils. The analysis was carried out using the PLAXIS 2D software, a finite element model, to examine the behavior of the surrounding soils and structures at different construction stages with the specific conditions of the underlying soils and loading conditions. The results reveal that safety factors range from 1.19 to 1.25 for different considered phases, well above the design value of 1.125 l as stipulated in the standard QCVN 04–05:2022/BNNPTNT. The maximum lateral displacement of the sheet pile wall was 10.61 cm, which is well within the acceptable value of 12 cm. Maximum sheet-piling moments for the SW600A and SW350A sheet-piles were 207.2 kNm and 106.1 kNm, respectively, below their acceptable bending capacity.